The use of ball joints allows pivoting movement of the suspension and steering components relative to each other while retaining the capacity to transmit axial and shear forces to accommodate wheel movement, steering movement and maintain wheel alignment.
For example, a MacPherson strut suspension uses a substantially vertical strut housing a shock absorber and spring to connect a wheel hub carrier or knuckle to an automotive body. The strut can rotate about a vertical axis to provide steering for the wheel and a lower control arm is necessary to hold the lower end of the strut in position to resist lateral movement. The inboard end of the control arm is hinged to the automotive chassis and the outboard end is connected to the wheel hub carrier with a ball joint. Excessive wear of the ball joint bearings results in steering, suspension and wheel alignment inaccuracy which is corrected by replacement of the ball joint.
Manufacturers involved in the design of automotive aftermarket parts often seek to improve upon the original equipment manufacturer's designs (OEM) when providing replacement parts. A purchaser, such as an auto repair shop, can simply replace a worn part with an identical new part manufactured to the specifications of the original equipment manufacturer (OEM). However improvements are desirable to avoid merely repeating the same premature wear experienced with the OEM part and to enhance the aftermarket manufacturer's market share by providing the purchaser with a performance improvement incentive to purchase from the aftermarket manufacturer instead.
Any improved replacement part must approximate the original mass of the OEM suspension since significant alteration of the mass could detrimentally effect the operation of the suspension. The improved replacement part must also be limited to the space provided in the OEM vehicle to avoid the need to modify adjacent components and prevent interference.
An example of accelerated wear and deterioration is seen in the suspension and steering system of a vehicle having a control arm forged or cast of a lightweight non-ferrous material such as aluminum where the outboard end includes a ball joint mounted in a socket with polymer bearings. Various factors of the OEM design contribute to accelerated wear, premature failure and repair expenses.
Severe space restrictions in the suspension and steering designs of some vehicles exist where the ball joint and outboard end of the control arm are located relatively close to the adjacent brake rotor. The limited space available reduces the ability to improve the design by taking the obvious route of simply increasing material around the outboard end of the control arm. Space is extremely limited to the extent that the OEM has opted in some cases to cut out an adjacent portion of the brake rotor shield to allow more space for the ball joint and control arm.
The ball joint is exposed to high temperature caused by the close proximity to the brake rotor. Generally a brake disc shield is provided about the brake rotor to reduce heat transfer to adjacent vehicle parts and to prevent exposure of moving parts to brake dust particles generated during the wearing of the brake pads against the brake rotor. Polymer bearings deteriorate in high heat conditions. The abrasive brake dust penetrates into the ball joint and is captured in the lubricant between moving parts which causes increased wearing of the polymer bearings. The removal of a portion of the brake shield in some designs provides more space for the ball joint and outboard end, but also results in increased exposure of the ball joint to heat and dust which accelerates wear.
The choice of polymer bearings for the ball joint combined with increased exposure to heat and dust from braking therefore has resulted in premature failure. Brake dust, road salt and sand particles can penetrate the seals of a ball joint and mix with the lubricant grease. The wear experienced by the polymer bearing is accelerated and causes excessive axial and radial play in the ball joint.
A control arm assembly uses forged or cast non-ferrous or aluminum control arms with a socket machined in the outboard end to house polymer bearings and ball stud of the ball joint. The OEM control arm assembly has a low weight, low cost and is simple to manufacture. Accelerated wear results however from the design choices made by the OEM. The low weight and low cost OEM design limits the adoption of aftermarket improvements to extend the cycle life of the control arm assembly, since improvements generally add material or add weight or both.
For example, the aftermarket parts industry has improved ball joint lifespan and durability by using sintered metal bearings manufactured from metal powder which have advantages over polymer bearings. Sintered metal bearings are porous and the lubricant penetrates the bearing surfaces improving lubrication of the surfaces of adjacent moving parts. Sintered metal is more durable at lower temperatures better than polymers and withstands high temperature environments better than polymers. Sintered metal has better wear characteristics than polymers and sintered metal does not degrade due to chemical incompatibility with grease formulations like polymers.
Replacement of sintered bearings for the polymer bearings of an OEM control arm assembly is relatively simple when done by a replacement parts manufacturer.
Bearing replacement is impractical and uneconomical for a mechanic other than during replacement of an entire manufactured ball joint or control arm assembly consisting of a preassembled control arm and ball joint. Using the OEM geometry and functional dimensions of the OEM control arm assembly, sintered metal bearings are located with the ball stud in a socket of a replacement control arm. However when a non-ferrous or aluminum control arm is used, use of press fit sintered hardened metal bearings would quickly wear away at the adjacent softer control arm material of the socket during operation. Press fitting of sintered metal bearings also exerts an additional radial stress and circumferential tensile stresses on the adjacent aluminum material of the control arm socket which is not experienced with low strength polymer bearings.
It is desirable to extend the cycle life of the ball joint, to avoid overstressing of the outboard end of the aluminum control arm in which the ball joint is mounted, maintain use of a light weight non-ferrous or aluminum control arm, maintain dimensional clearances between the ball joint, the control arm and adjacent components during operation and to maintain components in their original OEM alignment.
Features that distinguish the present invention from the background art will be apparent from review of the disclosure, drawings and description of the invention presented below.